JavaScript实现Base64编码转换

define(function(require, exports, module) {
 
  var code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".split(""); //索引表
 
  /**
   * @author laixiangran@163.com
   * @description 将二进制序列转换为Base64编码
   * @param {String}
   * @return {String}
   */
  function binToBase64(bitString) {
    var result = "";
    var tail = bitString.length % 6;
    var bitStringTemp1 = bitString.substr(0, bitString.length - tail);
    var bitStringTemp2 = bitString.substr(bitString.length - tail, tail);
    for (var i = 0; i < bitStringTemp1.length; i += 6) {
      var index = parseInt(bitStringTemp1.substr(i, 6), 2);
      result += code[index];
    }
    bitStringTemp2 += new Array(7 - tail).join("0");
    if (tail) {
      result += code[parseInt(bitStringTemp2, 2)];
      result += new Array((6 - tail) / 2 + 1).join("=");
    }
    return result;
  }
 
  /**
   * @author laixiangran@163.com
   * @description 将base64编码转换为二进制序列
   * @param {String}
   * @return {String}
   */
  function base64ToBin(str) {
    var bitString = "";
    var tail = 0;
    for (var i = 0; i < str.length; i++) {
      if (str[i] != "=") {
        var decode = code.indexOf(str[i]).toString(2);
        bitString += (new Array(7 - decode.length)).join("0") + decode;
      } else {
        tail++;
      }
    }
    return bitString.substr(0, bitString.length - tail * 2);
  }
 
  /**
   * @author laixiangran@163.com
   * @description 将字符转换为二进制序列
   * @param {String} str
   * @return {String}  
   */
  function stringToBin(str) {
    var result = "";
    for (var i = 0; i < str.length; i++) {
      var charCode = str.charCodeAt(i).toString(2);
      result += (new Array(9 - charCode.length).join("0") + charCode);
    }
    return result;
  }

  /**
   * @author laixiangran@163.com
   * @description 将二进制序列转换为字符串
   * @param {String} Bin
   */
  function BinToStr(Bin) {
    var result = "";
    for (var i = 0; i < Bin.length; i += 8) {
      result += String.fromCharCode(parseInt(Bin.substr(i, 8), 2));
    }
    return result;
  }
  exports.base64 = function(str) {
    return binToBase64(stringToBin(str));
  }
  exports.decodeBase64 = function(str) {
    return BinToStr(base64ToBin(str));
  }
})

function getCanvas(w, h) {
  var c = document.createElement('canvas');
  c.width = w;
  c.height = h;
  return c;
}
 
function getPixels(img) {
  var c = getCanvas(img.width, img.height);
  var ctx = c.getContext('2d');
  ctx.drawImage(img, 0, 0);
  return ctx.getImageData(0, 0, c.width, c.height);
}

function img2Base64(img) {
  var imgData = getPixels(img).data;
  var imgWidth = getPixels(img).width;
  var imgHeight = getPixels(img).height;
  var bin = "";
  for (var i = 0; i < imgData.length; i++) {
    bin += base.numToString(imgData[i]);
  }
  bin = bin + base.stringToBin("$$" + imgWidth + "," + imgHeight + "$$");
  return base.binToBase64(bin);
}

function paint(imgData) {
    var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    ctx.fillRect(0, 0, imgData.width, imgData.height);
    ctx.putImageData(imgData, 0, 0);
  }
 
function base642img(data) {
  var str = base.BinToStr(base.base64ToBin(data));
  var imgWidth = str.match(/\$\$(\d+),(\d+)\$\$$/, "")[1];
  var imgHeight = str.match(/\$\$(\d+),(\d+)\$\$$/, "")[2]
  var imgData = base.base64ToBin(data).replace(base.stringToBin("$$" + imgWidth + "," + imgHeight + "$$"), "");
 
  var ImageDataArray = new Uint8ClampedArray(imgWidth * imgHeight * 4);
  for (var i = 0; i < ImageDataArray.length; i++) {
    ImageDataArray[i] = parseInt(imgData.substr(i * 8, 8), 2);
  }
  return new ImageData(ImageDataArray, imgWidth, imgHeight);
 
}